Let me say straight up that yards per carry is a fine stat. Is it descriptive of a player’s true skill level and not his environment? Sometimes yes, mostly no. But this isn’t fantasy baseball. True skill level is illusory. The productivity of all of our players is, to a very large degree, a function of their environment.

But play success rate is useful in measuring running back performance not because it alters this reality of fantasy football that environment is king (it does not reveal true skill level any better than yards per carry in comparing players on different teams) but because it’s a hidden metric. The teams use it, of course, but we don’t have access to it easily.

But here, I’m using Pro-Football-Reference play-by-play data to figure out whether a run was successful or not. It’s binary. If you gain 40% of the distance on first down, half the distance on second down or convert a third down or fourth down, the play is a success. If you rush for...